Olefin polymerization catalyst

ABSTRACT

Olefin polymerization catalysts are prepared by depositing an organophosphoryl chromium product and an aluminum acetyl acetonate on an inorganic support material, and heating the support material in a non-reducing atmosphere at a temperature above about 300° C. up to the decomposition temperature of the support material.

This application is a continuation-in-part of copending application Ser.No. 724,484 filed Sept. 20, 1976 which in turn is a continuation-in-partof Ser. No. 558,504 filed Mar. 15, 1975, now U.S. Pat. No. 3,984,351.

BACKGROUND OF THE INVENTION

The use of chromium compounds in the polymerization of olefins iswell-known. U.S. Pat. Nos. 2,825,721 and 2,951,816 teach the use of CrO₃supported on an inorganic material such as silica, alumina orcombinations of silica and alumina and activated by heating at elevatedtemperatures to polymerize olefins. When these catalyst systems are usedin various polymerization processes such as the well-known particle-formprocess, the resins produced, while useful in many applications, areunsatisfactory for others because of a deficiency in certain propertiessuch as melt index.

Attempts to improve deficient properties of polyolefins produced usingsupported, heat-activated chromium oxide catalysts have been made byadding various metal and non-metal compounds to the supported chromiumoxide prior to activation by heating. For example, in U.S. Pat. No.3,622,522 it is suggested that an alkoxide of gallium or tin be added tosupported chromium oxide prior to heat activation. U.S. Pat. No.3,715,321 suggests adding a compound of a Group II-A or Group III-Bmetal to supported chromium oxide prior to heat treatment whereas U.S.Pat. No. 3,780,011 discloses adding alkyl esters of titanium, vanadiumor boron and U.S. Pat. No. 3,484,428 discloses adding alkyl boroncompounds.

In columns 5 and 6 and Table 1 of U.S. Pat. No. 3,622,522 the additionof aluminum isopropoxide to supported chromium oxide prior to heatactivation is shown for purposes of comparison with the addition of analkoxide of gallium or tin. The patentee concluded that the addition ofthe aluminum compound gave substantially the same or an increasedHLMI/MI ratio of polymers produced as compared to the chromium oxidecatalyst with no metal alkoxide added, whereas the addition of galliumor tin alkoxides produced polymers having a lower HLMI/MI ratio.

It is also known to utilize other chromium compounds as catalysts forthe polymerization of olefins. Such compounds include various silylchromate and polyalicyclic chromate esters as described, for example, inU.S. Pat. Nos. 3,324,095; 3,324,101; 3,642,749; and 3,704,287. The useof phosphorus-containing chromate esters in olefin polymerizationcatalysts has also been disclosed in the aforesaid U.S. Pat. No.3,704,287; and in U.S. Pat. No. 3,474,080 and copending application Ser.No. 532,131, filed Dec. 16, 1974, now U.S. Pat. No. 3,985,676.

Use of the above chromium compound catalysts in Ziegler-typecoordination catalyst systems has also been proposed. As is well-knownin the art, such catalysts frequently additionally compriseorganometallic reducing agents such as, for example, trialkyl aluminumcompounds. Ziegler-type catalyst systems incorporating supportedchromium compound catalysts and organometallic reducing agents,particularly organoaluminum compounds, are disclosed, for example, inU.S. Pat. Nos. 3,324,101; 3,642,749; 3,704,287; 3,806,500; and U.S. Pat.No. 3,985,676.

SUMMARY OF THE INVENTION

It has been discovered in accordance herewith that olefin polymers, ofsuitable properties e.g. melt indexes and melt index ratios, may besecured at acceptable productivity levels by utilization of an olefinpolymerization catalyst system prepared by depositing anorganophosphoryl chromium product and aluminum acetylacetonate compoundon an inorganic support material and heating the supported chromiumcontaining product and aluminum compound at a temperature above 300° C.up to the decomposition temperature of the support. The heat treated,supported chromium containing product and aluminum compound may beemployed directly as an olefin polymerization catalyst. Polymersproduced using the novel catalyst systems of the present invention havedesirable flow properties and shear response.

DETAILED DESCRIPTION OF THE INVENTION

The novel catalyst systems of the present invention are prepared bydepositing, on an inorganic support material having surface hydroxylgroups, aluminum acetylacetonate compound and an organophosphorylchromium product. The supported chromium containing product and aluminumcompound are then heated in a non-reducing atmosphere at a temperatureabove about 300° C. up to the decomposition temperature of the supportmaterial.

It is believed that the chromium containing product and the aluminumcompound react with the surface hydroxyl groups on the inorganic supportmaterial during the course of preparing the novel catalyst systems ofthe present invention. However, the precise mechanism involved is notknown and applicants do not wish to be restricted to the mechanismpostulated above.

The inorganic support materials useful in the present invention includethose normally employed in supported chromium catalysts used in olefinpolymerizations such as those discussed in U.S. Pat. No. 2,825,721.Typically, these support materials are inorganic oxides of silica,alumina, silica-alumina mixtures, thoria, zirconia and comparable oxideswhich are porous, have a medium surface area, and have surface hydroxylgroups. Preferred support materials are silica xerogels or xerogelscontaining silica as the major constituent. Especially preferred are thesilica xerogels described in U.S. Pat. No. 3,652,214 which silicaxerogels have a surface area in the range of 200 to 500 m² /g, a porevolume greater than about 2.0 cc/g, a major portion of the pore volumebeing provided by pores having diameters in the range of 300 to 600 A.

The chromium containing compounds useful in the present inventioncomprise the organophosphoryl chromium compounds disclosed in applicantsU.S. Pat. No. 3,985,676 (incorporated herein by reference) whichcomprise the reaction product of chromium trioxide with anorganophosphorus compound having the formula: ##STR1## wherein R isalkyl, aralkyl, aryl, cycloalkyl or hydrogen, but at least one R isother than hydrogen. The preferred organophosphorus compounds aretrialkyl phosphates such as triethyl phosphate.

The aluminum acetylacetonate for deposition on the inorganic supportmaterials herein is commercially produced and widely available,including grades which can be advantageously employed in catalysis.

The novel catalysts of the present invention may be prepared bydepositing the organophosphoryl chromium product and the aluminumcompound on the inorganic support in any suitable manner such as byvapor coating or by impregnating the support with solutions thereof in asuitable inert solvent which is normally an anhydrous organic solvent.Such organic solvents include aliphatic, cycloalkyl, and alkylarylhydrocarbons and their halogenated derivatives. A preferred organicsolvent is dichloromethane. The chromium containing-product may beapplied to the support first or the aluminum compound may be appliedfirst or the chromium and aluminum compound may be applied together. Inapplicants' usual method of catalyst preparation, the support isimpregnated first with the chromium-containing product and then thealuminum compound.

Preferably the organoaluminum compound may be applied to the catalystsupport under conditions similar to those utilized for deposition of theorganophosphoryl chromium compound.

The most effective catalysts have been found to be those containing thechromium in an amount such that the amount of Cr by weight based on theweight of the support is from about 0.25 to 2.5% and preferably is fromabout 0.5 to 1.25%, although amounts outside of these ranges still yieldoperable catalysts. The aluminum compound should be added in sufficientamounts to provide from about 0.1 to 10% of aluminum by weight based onthe weight of the support and preferably from about 0.5 to 5.5% althoughother amounts outside of these ranges can be used to prepared operablecatalysts.

After the chromium containing product and the aluminum compound havebeen deposited on the inorganic support, the support is heated in anon-reducing atmosphere, preferably in an oxygen containing atmosphere,at a temperature above about 300° C. up to the decomposition temperatureof the support. Typically, the supported compositions are heated at atemperature of from 500° to 1000° C. The heating time may vary, forexample, depending on the temperatures used, from 1/2 hour or less to 50hours or more. Normally the heating is carried out over a period of 2 to12 hours. The nonreducing atmosphere which is preferably air or otheroxygen containing gas should be dry and preferably should bedehumidified down to a few parts per million (ppm) of water to obtainmaximum catalyst activity. Typically, air used in the proceduredescribed in this application is dried to less than 2-3 ppm of water.

It is also within the scope of the present invention to deposit thealuminum acetylacetonate upon the support followed by a firstheat-activation step and thereafter to deposit the chromium compoundupon the support followed by a second heat-activation step as in thedouble activation procedure described in U.S. Pat. No. 4,100,104,incorporated herein by reference. Double activation of the catalystsherein has been observed to provide still further increases in polymermelt indexes.

In accordance with the alternative double activation treatment of thecatalysts herein, the aluminum acetylacetonate is first deposited uponthe support as in the above-described single activation procedure andthe coated support is initially heated in a non-reducing atmosphere,preferably in a dry oxygen-containing atmosphere, at temperatures of atleast about 130° C., and up to the decomposition temperature of thesupport. Typically, the aluminum acetylacetonate-coated support isheated at a temperature of from about 130° C. to about 1100° C., andpreferably from about 260° C. to about 820° C. The period required forthe initial heating operation varies, depending upon the temperaturesutilized, from one-half hour or less, to about 50 hours or more, andnormally, is effected over a period of from about 2 to about 12 hours.Double activation is completed by thereafter depositing theorganophosphoryl chromium compound upon the aluninum-containing supportin the manner previously described for the single activation procedureand heating the thus treated support in a preferably dryoxygen-containing atmosphere, at temperatures above about 430° C. up tothe decomposition temperature of the support. Activation is suitablycarried out at temperatures of from about 430° C. to about 1100° C.,best results having been obtained by activation at temperatures of fromabout 840° C. to about 990° C. Activation can be carried out in this,the final heating operation, for periods varying from about one-halfhour or less to 50 hours or more, and most frequently, for periodsvarying from about 2 to about 12 hours.

The heat-treated supported chromium and aluminum materials of thepresent invention may be used directly as an olefin polymerizationcatalyst i.e., in the absence of a reducing agent as shown in theExamples. Such catalysts may also of course be employed in combinationwith metallic and/or non-metallic reducing agents as disclosed andclaimed in parent appln. Ser. No. 558,504, now U.S. Pat. No. 3,984,351.

The catalyst composition of this invention are amenable to use withconventional polymerization processes for olefins, in particular1-olefins having 2-8 carbon atoms and are suitable for polymerizationeffected under temperature and pressure conditions generally employed inthe art, e.g., temperatures of from about 40° C. to about 200° C. andpreferably from about 70° C. to 110° C. and pressures of from 200 to1000 psig and preferably from 300 to 800 psig, as are used in slurry orparticule form polymerizations.

CATALYST PREPARATION I. Single Activation Procedure

A. Silica gel having a pore volume of about 2.5 cc/g prepared inaccordance with the disclosure in U.S. Pat. No. 3,652,215 is added to a2000 ml, three-neck round bottom flask equipped with a stirrer, nitrogeninlet and y-tube with water condenser. A nitrogen atmosphere ismaintained during the coating operation. Dichloromethane is then addedto the flask containing the silica gel and stirring is commenced toinsure uniform wetting of the gel. A dichloromethane solution of thereaction product of CrO₃ and triethyl phosphate prepared as described inU.S. Pat. No. 3,985,676 is then added to the flask in sufficientquantity to provide a dry coated catalyst containing about 1% by weightof Cr. The supernatant liquid is removed by filtration and the coatedgel is dried in a rotary evaporator at 60° C. and with 29 inches of Hgvacuum.

B. Dichloromethane is added to a similar flask as used in Step A andwhile maintaining a nitrogen atmosphere stirring is commenced. To theflask is added the supported chromium composition prepared in step Aabove. A solution of dichloromethane and aluminum acetylacetonate isprepared in a pressure equalizing dropping funnel and the funnelattached to the stirred flask. The aluminum acetylacetonate solution isgradually added to the flask at the rate of 10 grams of solution perminute. After the addition of the solution is complete the slurry in theflask is stirred for about 1 hour. The supernatant liquid is removed byfiltration and the coated gel is dried in a rotary evaporator attemperatures up to about 60° C. and 29 inches Hg vacuum. The amount ofaluminum compound added depends on the % aluminum desired for theproduction of olefin polymers having specific properties necessary forcertain end use applications. In this case, an amount of aluminumacetylacetonate is added to provide a dry coated catalyst containing3.7% by weight of aluminum.

C. To heat activate the catalyst composition prepared in step B, thesupported catalyst is placed in a cylindrical container and fluidizedwith dry air at 0.20 feet per second superficial lineal velocity whilebeing heated to a temperature of 900° C. and held at this temperaturefor six hours. The activated supported catalyst is recovered as apowder.

II. Double Activation Procedure

A. The same procedure for preparing the dichloromethane slurry of silicagel in the abovedescribed single activation procedure is repeated(approximately 8 g dichloromethane per g of silica gel), however,omitting the deposition of the CrO₃ and triethyl phosphate reactionproduct.

B. A dichloromethane solution of aluminum acetylacetonate is depositedupon the wetted silica gel support of step A and the dry coated supportis recovered in the same manner described in step B of the singleactivation procedure.

C. The aluminum acetylacetonate coated support is placed in acylindrical container fluidized with dry air at 0.20 feet per secondsuperficial lineal velocity while being heated in steps to a temperatureof about 540° C. After six hours at this temperature, the initiallyactivated catalyst is permitted to cool under nitrogen and thenrecovered as a free flowing powder.

D. The powder obtained in step C is re-slurried in dichloromethane as instep A and coated with a solution of the reaction product of CrO₃ andtriethyl phosphate in dichloromethane in sufficient quantity to providea dry coated gel containing about 0.9% weight of Cr. The dichloromethaneis then stripped from the coated gel under vacuum.

E. The aluminum-containing, chromium-containing gel of step D isheat-activated for a second time at 890° C. in the same manner as instep C of the single activation procedure.

In the following Table, a series of polymerizations were carried toillustrate the results obtained from employing a chromium-containingcatalyst prepared with aluminum acetylacetonate modifier in accordancewith the single and double activation procedures described herein, andchromium-containing catalysts heretofore employed in the preparation ofolefins.

                                      TABLE                                       __________________________________________________________________________                          Productivity                                            Catalyst.sup.a  H.sub.2                                                                             (g polyethylene/g                                                                         Powder Resin Properties                     Example         (psi) cat. hr)    MI.sup.d                                                                             HLMI.sup.e /MI                       __________________________________________________________________________    1. Reaction product of                                                                        30    800         0.26   98                                     CrO.sub.3 and triethyl                                                                      120   400         0.48   88                                     phosphate                                                                   2. Same as Example 1 but                                                                      30    760         7.2    90                                     modified with aluminum                                                                      120   750         20     --                                     sec-butoxide.                                                               3. Same as Example 1 but                                                                      30    527         8.5    63                                     modified with aluminum                                                                      30    459         8.8    68                                     acetylacetonate as in                                                                       30    889         8.1    70                                     the Single Activation                                                                       120   675         30.4   --                                     Procedure herein                                                                            120   626         157    --                                                   120   600         22.4   --                                                   120   385         35.1   --                                   4. Same as Example 2 but                                                                      30    748         38     --                                     double activated..sup.b                                                                     120   (c)         --     --                                   5. Same as Example 3 but                                                                      30    593         17.0   --                                     double activated as                                                                         30    580         20.6   --                                     described herein..sup.b                                                                     30    396         45.6   --                                                   30    706         15.9   --                                                   120   543         43     --                                                   120   630         20.2   --                                                   120   869         27     --                                                   120   731         28.4   --                                   __________________________________________________________________________     .sup.a Al modifications at 3.7 wt. %                                           .sup.b Silica gel coated with Al compound was precalcined at 540°     C.                                                                            .sup.c No data available                                                      .sup.d Melt Index, ASTMD-1238, Condition E                                    .sup.e High Load Melt Index, ASTMD-1238, Condition F                          Reactor Conditions                                                            reactor temperature 210° F. isobutane solvent ethylene 10 mole         percent triethyl borane (15% in hexane at 0.5 cc per g catalyst          

According to the above data, the aluminum acetylacetonate modifiedcatalysts of this invention (Examples 3 and 5) possess good productivityand levels of hydrogen response comparable to those provided by thealuminum sec-butoxide modified catalysts (Examples 2 and 4). The HLMI/MI ratios of the polyethylenes obtained with the catalysts of thisinvention are lower than those obtained with the catalysts of Examples 1and 2 indicating a narrower molecular weight distribution for thepolyethylenes herein.

What is claimed is:
 1. A process for preparing an olefin polymerizationcatalyst system which comprises:(a) depositing an organophosphorylchromium reaction product of chromium trioxide and a phosphorus compoundhaving the formula ##STR2## wherein R is alkyl, aralkyl, aryl,cycloalkyl, or hydrogen but at least one R is other than hydrogen, upona solid inorganic support material; (b) depositing aluminumacetylacetonate upon said support material; and, (c) heat-activatingsaid supported organophosphoryl chromium reaction product and aluminumacetylacetonate in a non-reducing atmosphere at a temperature aboveabout 300° C. up to the decomposition temperature of the supportmaterial.
 2. The process for preparing a catalyst system according toclaim 1 wherein the aluminum acetylacetonate is first deposited upon thesupport material and the thus treated support is heat-activated in anon-reducing atmosphere at a temperature of at least about 130° C. up tothe decomposition temperature of the support and the organophosphorylchromium reaction product is thereafter deposited upon the support andthe thus treated support is again heat-activated but at a temperatureabove about 300° C. up to the decomposition temperature of the support.3. The process for preparing a catalyst system according to claim 1 or 2wherein said support material contains silica gel.
 4. The process forpreparing a catalyst system according to claim 2 wherein said silica gelis a silica xerogel having a surface area in the range of about 200 toabout 500 m² /g and a pore volume greater than about 2.0 cc/g, a majorportion of the pore volume being provided by pores having diameters inthe range of from about 300 to about 600 angstrom units.
 5. The processfor preparing a catalyst system according to claim 1 or 2 wherein theorganophosphoryl chromium reaction product is derived from the reactionof chromium trioxide and triethyl phosphate.
 6. The process forpreparing a catalyst system according to claim 1 or 2 wherein a metallicand/or non-metallic reducing agent is added to the heat-activatedcatalyst.
 7. The process for preparing a catalyst system according toclaim 6 wherein the reducing agent is a metallic reducing agent selectedfrom the group consisting of triethyl aluminum, triisobutyl aluminum,alkyl aluminum halide, alkyl aluminum alkoxide, dialkyl zinc, dialkylmagnesium and metal borohydride.
 8. The process for preparing a catalystsystem according to claim 6 in which the reducing agent is anon-metallic reducing agent selected from the group consisting of alkylborane and hydrides of boron.
 9. The process of preparing a catalystsystem according to claim 8 wherein the alkyl borane is triethyl borane.10. The process of preparing a catalyst system according to claim 1 or 2wherein the organophosphoryl chromium reaction product is present in anamount sufficient to provide about 0.25 to about 2.5% by weight of Crbased upon the weight of the support material and the aluminumacetylacetonate is present in an amount sufficient to provide about 0.10to about 10% by weight of Al based upon the weight of the supportmaterial.
 11. The olefin polymerization catalyst system produced by theprocess of claim 1 or
 2. 12. The olefin polymerization catalyst of claim11 to which a metallic and/or non-metallic reducing agent is added.